To reduce fuel consumption, an idling stop control in which idling is stopped while a vehicle is stopped, for example, to wait for the stoplight to turn, begins applying to vehicles. In this case, the engine must be restarted certainly when a driver start the vehicle. Accordingly, when an engine temperature when the engine is about to be stopped by the idling stop control is lower than a predetermined temperature, which makes it difficult to restart the engine, the idling stop is not carried out.
In the case of a diesel engine, the temperature within each cylinder is increased by using a glow plug. Glow plug control when restarting a stopped engine by idling stop control, has been suggested (refer to, for example, Japanese Unexamined Patent Publications Nos. 2004-176569, 6-257484, 2003-293926, and 2002-349370).
The above suggestion relates to control for reducing electric power consumption of the glow plug. Accordingly, though there is no clear description, when the engine is provided with a start improvement device such as a glow plug or an intake air heating device for heating intake air, even if an engine temperature when the engine is about to be stopped by the idling stop control is lower than a usual temperature predetermined when the engine is not provided with a start improvement device, the engine can be restarted by the improvement of the engine restart. Therefore, when the engine is provided with a start improvement device, a threshold value of the engine temperature for determining if the idling stop is carried out is set lower than the usual predetermined temperature.
Accordingly, when the engine is provided with a start improvement device, even if the engine temperature when the engine is about to be stopped by the idling stop control is relatively low, the idling stop can be carried out. However, if the start improvement device does not function normally, an engine stopped by the idling stop cannot be restarted easily.
Therefore, an object of the present invention is to provide a device, for controlling the idling stop of an engine, in which idling stop is carried out when the engine temperature of an engine that is about to be stopped by the idling stop control is higher than a threshold value, and which allows an engine to be restarted even if a start improvement device does not function normally.